Amplifiers are classified based on certain operating characteristics. For example, Class A amplifiers conduct signal current throughout the cycle of the signal wave, i.e., have 360 degree conduction. Class B amplifiers conduct signal current for exactly one half the cycle of the current waveform, i.e., 180 degree conduction. Class AB amplifiers are Class B amplifiers with a bias voltage to avoid cross-over distortion, and Class C amplifiers have more than 180 degree conduction and resonant loading.
Class D amplifiers have zero degree conduction and utilized switched power stage transistors to prevent the amplifier from entering the active region. These amplifiers are frequently included in audio systems such as home theater systems, mobile phones, and speakers. However, conventional Class D amplifiers suffer from limited linearity and require high precision analog components and analog control loops that are difficult to design.